Natural borneol improves cellular uptake of curcumin to enhance its photodynamic bactericidal activity against Escherichia coli ATCC 8739

Abstract

Photodynamic inactivation (PDI), a non-thermal sterilization method, has attracted considerable attention due to its broad-spectrum antimicrobial activity, environmental friendliness and cost-effectiveness. Curcumin (Cur), a food-grade photosensitizer, exhibits photodynamic antimicrobial activity based primarily on its efficiency in intracellular accumulation. However, Cur's low water solubility and the barriers presented by the outer membrane of Gram-negative bacteria challenge its ability to penetrate the cytoplasm. Natural borneol (NB), a monoterpene food flavoring agent, has also been shown to improve the efficiency of drug absorption. In this study, we demonstrated that NB significantly improved the cellular uptake of Cur, thereby enhancing its photodynamic bactericidal activity against Gram-negative Escherichia coli (E. coli) ATCC 8739, a potential alternative to enterohemorrhagic E. coli O157:H7. This effect was attributed to NB's ability to disrupt the integrity of the E. coli bacterial membrane, thereby increasing cellular permeability. Transcriptomic analysis further confirmed that NB dysregulated the expression of genes associated with bacterial membrane structure and function in E. coli. Consequently, the increased accumulation of Cur in E. coli led to excessive production of intracellular reactive oxygen species (ROS) upon exposure to 6.5 J/cm² blue light (BL). These ROS, analyzed biochemically and transcriptionally, primarily disrupted bacterial membrane structure and function, the antioxidant system, and ultimately caused bacterial death. Remarkably, this combined strategy not only reduced E. coli contamination in the tested orange juice, but also preserved its nutritional quality. In conclusion, this research provides an innovative and effective approach to maintaining food safety.